1. Field of the Invention
The present invention relates to an optical potentiometer for detecting the displacement of an object and a manipulator including the optical potentiometer.
2. Description of the Related Art
A medical manipulator is used in laparoscopic or thoracoscopic surgery. The medical manipulator generally includes a joint on the distal end side and a surgical instrument (for example, the grasp portion of a forceps or the like) at a portion nearer to the distal end than the joint.
In the manipulator having such an arrangement, a power generated by a driving source (for example, a motor or the like) is transmitted to the joint by a power transmission member (for example, a linear member such as a wire) to displace the joint. Such a power transmission mechanism opens/closes the grasp portion of the forceps or changes its orientation.
Note that the manipulator incorporates a guide member. The power transmission member is provided to be movable along the guide member.
In laparoscopic or thoracoscopic surgery using such a manipulator, a small incision is made in the abdominal part or the like of a patient. A jig called a trocar is attached into the incision. A medical manipulator is inserted from the insertion opening of the trocar, and the surgical instrument is operated to perform the surgery. The insertion opening of a currently used trocar has a diameter of about 10 mm or less. Hence, the diameter of the manipulator to be inserted from the trocar needs to be smaller than the diameter of the trocar. An example of the manipulator is a long (almost 300 mm or more) multi-degree-of-freedom manipulator having a small diameter of 10 mm or less represented by a da Vinci system available from Intuitive Surgical.
As the power transmission member, a linear member is used, as described above. The manipulator of the da Vinci system also uses a power transmission member such as a wire that is formed into a small diameter (for example, about 0.5 mm) to transmit a power in a limited space with a small diameter of 10 mm or less.
A technique associated with a manipulator using such a linear small-diameter power transmission member is disclosed in, for example, U.S. Pat. No. 5,807,377. That is, the manipulator of U.S. Pat. No. 5,807,377 is a manipulator that detects the position of the surgical instrument. U.S. Pat. No. 5,807,377 discloses a technique of detecting the displacement of the joint by a potentiometer or encoder arranged near the driving source such as a motor.
However, in the manipulator disclosed in U.S. Pat. No. 5,807,377, the driving source is disposed on the rear end side of the outer sheath. For this reason, the distance between the joint and the driving source becomes long, and the power transmission member disposed on the path essentially becomes long as well.
Additionally, the linear power transmission member for transmitting the power of the driving source to the joint has a very small diameter, as described above. For this reason, the power transmission member stretches or slackens under a tension. Accordingly, an error occurs between the driving amount of the driving source and the driving amount transmitted to the joint at the distal end. That is, when detecting the displacement of the joint by the potentiometer or encoder arranged near the driving source, the moving amount of the joint cannot accurately be detected because of the stretch or slack of the power transmission member, as described above. It is therefore difficult to detect the accurate position of the distal end of the surgical instrument.
For this reason, when getting the moving amount of the joint, the moving amount of the joint is preferably detected near the joint from the viewpoint of detection accuracy. However, in a surgical operation using the manipulator, the medical manipulator is inserted from the insertion opening of the trocar, as described above. Hence, the manipulator needs to have a small diameter (for example, 10 mm or less) for practical use. It is very difficult to provide a detection means (for example, a potentiometer, an encoder, or the like) in such a manipulator.